In U.S. Pat. No. 3,773,925, there is described and claimed the new polyene antibiotic partricin and a process of fermentation, extraction and purification for this new antibiotic. This antibiotic has a considerable antifungal and antiprotozoal activity.
According to the process described and claimed in U.S. Pat. No. 3,773,925, at the end of the fermentation stage, a tetracycline-type antibiotic which is produced simultaneously is extracted by acidifying the medium and filtering the aqueous phase which contains practically all the tetracycline-type antibiotic. At this stage, it is possible to extract the partricin from the mycelium by means of an appropriate solvent in which the antibiotic is soluble; in a typical process, the moist mycelium, containing diatomaceous earth or other filter aid, is suspended in butanol (about 100 - 400 liters butanol per 100 kg. of mycelium). The suspension is then adjusted, while stirring, to pH 9.2 - 10.2 by adding ammonium hydroxide or other appropriate base.
The mycelium is then removed by filtration and the butanolic solution of partricin is washed twice with a 5% aqueous solution of ethylenediamine-tetraacetic acid, previously adjusted to pH 9.8 with ammonium hydroxide.
After separating the aqueous phase, the butanolic solution is concentrated to a small volume (1/20 to 1/25 of the initial volume) at a reduced pressure and at a temperature no greater than 40.degree. to 45.degree. C. Partricin then crystallises out after cooling the solution.
In addition to butanol, the above-mentioned Patent also describes the use of other solvents, for example acetone, dimethyl sulphoxide, ethanol and the like.
It is known that the use of solvents for the extraction and purification of antibiotics on an industrial scale gives rise to a number of problems, both technical and economic. The installations needed to view of the inflammability and explosiveness of many organic solvents and organic solvent mixtures which are commonly employed must be of the anti-explosion type and considerable precautions have to be taken during the entire process of manufacture, especially if large volumes of solvents are used. At the end of the process, the solvents must be recovered, because of their extremely high cost, and rectified in installation, which are also expensive, and finally re-used.
Therefore, the initial cost of solvents and complex plant, the precautions, the storage of solvents, as well as the inevitable losses during processing, are all factors which have a marked adverse effect on the cost of the industrial process.
It is an object of the present invention to provide a new method for the extraction and purification of partricin which provides both practical and economic advantages.
The principal difficulty encountered in the extraction of polyene antibiotics from fermentation liquors is the low solubility of such antibiotics in most common organic solvents and their virtual insolubility in water.
Partricin is practically insoluble in water, is very sparingly soluble in most common organic solvents used on an industrial scale but is soluble in dimethylformamide, dimethylsulphoxide, dimethylacetamide and in pyridine, although not in very high concentrations.
The methods of extracting polyene antibiotics previously described in the literature are based mainly on the use of solvents which are miscible or immiscible with water and which almost always have a density lower than that of water, these solvents being added to the entire liquor or, more frequently, to the mycelium separated from the aqueous phase.
n-Butanol is the solvent which is usually preferred. When the extraction has been carried out, the solvent is generally separated from the exhausted mycelium and concentrated under reduced pressure to a small volume.
This latter operation is frequently preceded and followed by other extraction treatments, the purpose of which is to eliminate the greater part of the impurities present.
It is obvious that the extraction of large volumes of mycelium with solvents in which this class of antibiotics is not very soluble necessarily requires the use of large volumes of the solvents themselves.
The concentration of the extracts and the removal of the solvent impregnating the exhausted mycelium also constitute and economically disadvantageous feature in industrial production.
Such considerations, which also apply to the process of extracting the antibiotic partricin, have induced us to look for an alternative process which permits the use of considerably smaller volumes of organic solvents.